Do not turn down the brothers' offer of work or call them by the wrong names (Considering how easy it is to guess wrong, it's best to avoid names altogether).

Speak to Torr in Klamath and accept his quest to Guard the brahmin. You will then be transported to the pasture. Kill the first radscorpion you see, and then talk to the Dunton brothers who are to the west of Torr's encampment and accept their quest to make Torr leave. Alternatively, talk to the brothers at their shop in town, but do not refuse their offer or call either by their first name. Then, go to the pasture and tell Torr you will help him Guard the brahmin.